Do Model.find() on replicate MongoDB

Hi everyone i have a problem and i need to solve for my project of university. One of my teachers said i needed a replicate database but when i make a simple request Model.find() return a error message : Operation `users.find()` buffering timed out after 10000ms.

docker-compose.yml:

version: '3.1'
services:

  DB1:
    image: mongo:latest
    restart: always
    ports:
      - "21017:27017"
    env_file:
      - .env
    environment:
      MONGO_INITDB_ROOT_USERNAME: ${MONGO_ROOT_USR}
      MONGO_INITDB_ROOT_PASSWORD: ${MONGO_ROOT_PWD}
      MONGO_INITDB_DATABASE: test
    volumes:
      - dbdata6:/data/db

  DB2:
    image: mongo:latest
    restart: always
    ports:
      - "21018:27018"
    env_file:
      - .env
    environment:
      MONGO_INITDB_ROOT_USERNAME: ${MONGO_ROOT_USR}
      MONGO_INITDB_ROOT_PASSWORD: ${MONGO_ROOT_PWD}
      MONGO_INITDB_DATABASE: test
    volumes:
      - dbdata7:/data/db

code NodeJS:

const mongoose = require('mongoose');

async function Run() {


    var s = await mongoose.connect('mongodb://root:[email protected]:21017,127.0.0.1:21018/test',

        {
            authSource: "admin",
        }
    ).then(
        () => {
            console.log("Connected to MongoDB");
        },
        err => {
            console.error(err);
        }
    );

    console.log("Connected to MongoDB");
}

app.get(`/collectLastId`, async (req, res) => {
    var s = await require('../models/User.model.js').makeModel();

    var data = (await s.find({}));

    res.writeHead(200, { 'Content-Type': 'application/json' });
    res.end(s.toString());
});

I would like know how i can use Model.find() with two DB. Thanks!